It’s a bit of a meme, but this needs to be a real Second International party, not just a bunch of red-painted Populists. Synthesising Lincolnian tactics and Marxian doctrine in something similar to the Erfurt Program was the way to go in my view.
oh yes, I liked tracing how you outlined each swing in the theories they adopted, the SLPA/Workingmen's/Grangerite/Greenback coalition in the 80s, then the tension between the old union leaders, the Haymarket/Homestead unionists, Sewer Socialists, and Populists in the 90s, and then DeLeonism forming a bridge to the age of Debs and the Wobblies: each move marches along left-leg-right-leg
I got a lot of notes building up for an eventual "fix fic" and I'd say the Socialists are going to be externally shaped by Galleanist anarchists and the Democrats[1] who're now pro-German (at least when it comes to mobilization and training) and anti-Southern: so the SPA can 1. thread the needle between organized, disciplined labor militancy vs. just bomb-throwing, while also 2. facing down a revanchist, militarist Remembrance Party that by the turn of the century explicitly wants to make the country rise like a phoenix and establish the American Empire of the book title[2][3]
also Turtledove made much of Lincoln predicting any Southron revolution would be Black--presumably that they'd take the revolutionary road rather than by democratizing society
(I can also hear Flora Hamburger overhearing these considerations from the next room and yelling "it's not 'interesting,' it's
dialectical!" lol)
[1] my "TL-191.1" calls this era the "National Union Party" to make it seem bigger than just "the other party," underscore its ideological revamping, to mark a break with , and as an ironic nod to the Lincoln-Johnson ticket of 1864 OTL
[2] and the NUP itself will have its own needles to thread, since 1. its ideology is that which gave us the Palmer Raids and 1914 dachshund-kickings OTL, but 2. its base will be Papist hypenated-americans, machine bosses, and homicidal mine-owners
[3] my GOP's reduced to [on edit] Vermont, RI, and Maine 100% and popping up MI-IN-OH-PA and KS-NE, but still strong enough before the 1900s shuffles (which turn them "the Democrats" again for TR's Presidency) to field recognizable names like Garfield, John Sherman, Harrison, and (on the NUP ticket) Thomas Brackeet Reed, Jr., and Nelson Aldrich, and later Charles Fairbanks, Elihu Root, Leonard Wood